Downhole expandable drive reamer apparatus

ABSTRACT

A downhole expandable drive reamer apparatus is described. The apparatus comprises a body defining a longitudinal axis X-X. At least one roller is disposed on the body and is moveable relative to the body between an inwardly retracted condition and an outwardly deployed condition. A thread or other protrusion is formed on at least one roller and is arranged to engage a surface of a well bore to drive the apparatus to along the well bore when the roller is in the outwardly deployed condition. The rotational axis R-R of the roller is non-parallel to the longitudinal axis X-X of the body.

The present invention relates to a downhole expandable drive reamer apparatus for incorporation into a work string used in the recovery of hydrocarbons from well bores.

Downhole drill strings are used in the oil and gas industry to cut well bores to reach pockets of oil and gas. A drill string comprises lengths of elements called subs which are interconnected to lengthen the drill string as the drill string advances down a borehole.

To meet demand for energy, the drilling of oil and gas wells is becoming more and more complex in order to open up new reserves. Wells are drilled from land directionally and wells are also drilled in deeper and deeper formations. This means that drill strings can stretch up to several kilometres in length and may be curved to facilitate directional drilling. However, longer, directional drill strings are susceptible to becoming stuck which can cause a catastrophic failure of the drill string.

A particular problem that arises with directional drilling is that the drill string/pipe commonly does not rotate in an operation called “sliding” the pipe. A bit at the end of the string is rotated by a mud motor, but most of the length of the drill sting is stationary which greatly increases friction. This therefore increases the likelihood of the drill string becoming stuck.

A known downhole traction apparatus is described in WO2012/069795. This apparatus comprises a plurality of rollers mounted around a body adapted to be incorporated into a drill string. The rollers are mounted about axes offset from the longitudinal axis of the tool. The rollers are mounted in a bonded elastomeric element which is able to deform slightly outwardly in response to differential pressure in the tool bore deforming the elastomeric element. This enables the rollers to be pushed out of the tool body and against the sides of a wellbore.

The apparatus of WO2012/069795 suffers from several drawbacks. Firstly, the extent to which the rollers can grip the side of a wellbore to provide traction is limited because of the surface configuration of the rollers. Secondly, it is difficult to control the extent of outward deployment of the rollers in response to differential pressure acting on the elastomeric carrier element. Furthermore, high levels of differential pressure can also cause leakage through the seal of the elastomeric carrier element. Moreover, in some circumstances there is a limited amount of pump pressure available for pressurising the tool to deform the elastomeric element outwardly and deploy the rollers. In such a circumstance, the tool would be rendered useless.

A preferred embodiment of the present invention seeks to overcome the above disadvantages of the prior art.

According to an aspect of the present invention, there is provided a downhole expandable drive reamer apparatus for incorporation into a drill string, the apparatus comprising:

a body defining a longitudinal axis; at least one roller moveable relative to the body between an inwardly retracted condition and an outwardly deployed condition; surface engagement means disposed on an outer surface of said at least one roller, the surface engagement means comprising at least one protrusion extending from an outer surface of said at least one roller to engage a surface of a well bore to drive the apparatus along the well bore; characterised in that the rotational axis of said at least one roller is non-parallel to the longitudinal axis of the body.

This provides the advantage of an apparatus that can be incorporated into many types a drill string to assist movement of the drill string along a well bore with little intervention from operators on the surface. In particular, this apparatus can help to pull a non-rotating drill string down a hole when positioned on the bottom bearing mandrel of a down hole motor or mud motor, wherein the drill bit would mount to the bottom of the expandable drive reamer apparatus.

It has been found that by providing threaded, studded or rollers comprising some other form of surface engaging protrusion, wherein the rollers rotate about a longitudinal axis which is offset from the longitudinal axis of the body on which they are disposed, the rollers engage the surface of a well bore and pull the drill string along the well bore.

This is advantageous because the only activity required by the operators on the surface is to operate the apparatus to deploy the rollers to the outward condition to engage the surface of the well bore.

In a preferred embodiment, the angle formed between the rotational axis of said at least one roller and the longitudinal axis of the body is more than zero degrees and no more than five degrees.

It has been found that an angle of offset of between 0 and 5 degrees is most effective in providing a downward force on the apparatus to move the apparatus along a well bore.

Said at least one roller may be rotatably mounted between two pistons, each said piston being arranged to be moved between an inwardly retracted position in the body and an outwardly deployed condition relative to the body in response to pressurisation of fluid in the body.

This provides the advantage of making the apparatus straightforward for operators on the surface to activate. All that is required is to commence the pumping of fluid along the work string which will automatically deploy the rollers to the outward condition.

This also provides the advantage that the pistons provide a rigid construction that prevents leakage of fluid under pressure in the tool body. Furthermore, in situations where there is a limited amount of hydraulic force available for the deployment of rollers, the pistons provide a reliable deployment method of enabling operators to control the extent of deployment of the pistons. The pistons also help to prevent debris accumulating between the rollers and the tool body which results in a reliable tool that requires little maintenance and repair.

Said at least one roller may be rotatably mounted between two mounting members, each said mounting member being disposed on respective biasing means to enable each said mounting member to move between an inwardly retracted position in the body and an outwardly deployed condition relative to the body.

This provides the advantage of an assembly that does not operate in response to a change in fluid pressure, which means that there is no requirement for seals to prevent fluid escaping from the body. This removes any likelihood of the apparatus malfunctioning due to seal failure and having to be repaired. This also provides the advantage of ensuring that the rollers are deployed even in the event of low fluid pressure in the tool because deployment of the rollers is not dependent on pump pressure.

Said biasing means may comprise at least one disk spring mounted between the respective mounting member and the body.

In a preferred embodiment, the apparatus further comprises a plurality of rollers disposed at different locations around the body.

The surface engagement means may comprise a thread disposed on an outer surface of said at least one roller.

The surface engagement means may comprise a plurality of protrusions disposed on an outer surface of said at least one roller.

According to another aspect of the present invention, there is provided a drill string comprising a downhole expandable drive reamer apparatus as defined above.

A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:

FIG. 1 is a side view of a downhole expandable drive reamer apparatus of a first embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1;

FIG. 3 is a perspective view of the apparatus of FIGS. 1 and 2 showing the rollers in the outwardly deployed activated condition; and

FIG. 4 is a cross sectional view of a downhole expandable drive reamer apparatus of a second embodiment of the present invention.

Referring to FIG. 1, a downhole expandable drive reamer apparatus 2 for incorporation into a work or drill string comprises a body 4 defining a longitudinal axis X-X. At least one roller 6 is disposed on the body and is moveable relative to the body 4 between an inwardly retracted condition and an outwardly deployed condition.

Surface engagement means such as a thread 8 is formed on at least one roller 6 and is arranged to engage a surface of a well bore to drive the apparatus to along the well bore when the roller 6 is in the outwardly deployed condition. The rotational axis R-R of the roller 6 is non-parallel to the longitudinal axis X-X of the body as shown in FIG. 1.

In the example shown in the drawings, the surface engagement means is shown as a thread 8. However, it has been found that almost any type of outer profile on roller 6 engages the well bore surface and assists advancement of the apparatus along a well bore. For example, protrusions on the outer surface of the rollers 6, such as tungsten carbide studs press fit into the roller 6 have also been found to be effective.

In FIG. 1, the angular offset between axes X-X and R-R is shown as 5 degrees, but it has been found that the rollers provide the most downward force if the angle of offset is more than 0 degrees and no more than 5 degrees. The apparatus 2 is designed to be rotated by a mud motor at high RPM, such as 180 RPM. As a consequence, it has also been found that an offset of greater than 5 degrees could possibly stall the mud motor and advance the drive reamer apparatus 2 at too great a rate. Apparatus 2 is in the form of a sub to be interconnected into a drill string at its lower 4 a and upper 4 b ends. Each roller 6 is formed on an axle 10 which is rotatably mounted between two pistons 12 and 14.

Referring to FIG. 2, a longitudinal bore 16 is provided through the body 4 through which pressurised fluid such as drilling mud can flow. When surface operators pump pressurised fluid through bore 16, inner surfaces 18 of the pistons 12 and 14 are urged outwardly to deploy the pistons and therefore deploy the roller 6 to the outwardly deployed conditions. However, it will be apparent to persons skilled in the art that other mechanisms can be used to deploy the rollers outwardly, such as sliding mandrels.

A particular example of the operation of apparatus 2 in a non-rotational directional drill string in which apparatus 2 is mounted between the bottom bearing mandrel of a mud motor (not shown) and the drill bit (not shown) at the bottom end of a drill string. Apparatus 2 is rotated by the mud motor along with the bit. Rollers 6 are deployed to the outward expanded condition and provide a downward force by engaging and rolling against the walls of the well bore to assist downward advancement. When the string is to be retrieved, the rollers 6 are retracted.

Referring to FIG. 4, a downhole expandable drive reamer apparatus of a second embodiment of the present invention is shown with parts common to the embodiment of FIGS. 1 to 3 denoted by like referenced numerals but increased by 100.

Downhole expandable drive reamer apparatus 102 for incorporation into a work or drill string comprises a body 104 defining a longitudinal axis. At least one roller 106 is disposed on the body 104 and is movable between an inwardly retracted condition and an outwardly deployed condition. Surface engagement means such as thread 108 is disposed on the outer surface of the roller 106. In common with the embodiment of FIGS. 1 to 3, the rotational axis of the roller 106 is non parallel to the longitudinal axis of the body 104.

Roller 106 is mounted on an axle 110 between first and second mounting members 120 and 122. Each mounting member 120 and 122 is disposed on respective biasing means 124 and 126. In the embodiment shown, the biasing means 124 and 126 comprises a plurality of disc springs 128, although a single disk spring for each mounting member 128 could be used. Each mounting member is held in the body by use of a pin 130 mounted to the body and extending through a respective window 132 in the mounting member.

The use of biasing means 124 and 126 mounted externally on the body such as disc springs 128 provides the advantage that the roller 106 can move in and out relative to the body without the requirement for fluid pressure to act on any part of the assembly to push the roller outwards. This removes the requirement for any form of seals which can be costly to replace as a result of malfunction. Instead of disc springs 128, elastomeric elements might also be used to form biasing means 124 and 126.

It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. 

1. A downhole expandable drive reamer apparatus for incorporation into a drill string, the apparatus comprising: a body defining a longitudinal axis; at least one roller moveable relative to the body between an inwardly retracted condition and an outwardly deployed condition; surface engagement means disposed on an outer surface of said at least one roller, the surface engagement means comprising at least one protrusion extending from an outer surface of said at least one roller to engage a surface of a well bore to drive the apparatus along the well bore; characterised in that the rotational axis of said at least one roller is non-parallel to the longitudinal axis of the body.
 2. An apparatus according to claim 1, wherein the angle formed between the rotational axis of said at least one roller and the longitudinal axis of the body is more than zero degrees and no more than five degrees.
 3. An apparatus according to claim 1, wherein said at least one roller is rotatably mounted between two pistons, each said piston being arranged to be moved between an inwardly retracted position in the body and an outwardly deployed condition relative to the body in response to pressurisation of fluid in the body.
 4. An apparatus according to claim 1, wherein said at least one roller is rotatably mounted between two mounting members, each said mounting member being disposed on respective biasing means to enable each said mounting member to move between an inwardly retracted position in the body and an outwardly deployed condition relative to the body.
 5. An apparatus according to claim 4, wherein said biasing means comprises at least one disk spring mounted between the respective mounting member and the body.
 6. An apparatus according to claim 1, further comprising a plurality of rollers disposed at different locations around the body.
 7. An apparatus according to claim 1, wherein the surface engagement means comprises a thread disposed on an outer surface of said at least one roller.
 8. An apparatus according to claim 1, wherein the surface engagement means comprises a plurality of protrusions disposed on an outer surface of said at least one roller.
 9. (canceled)
 10. A drill string comprising a downhole expandable drive reamer apparatus according to claim
 1. 11. An apparatus according to claim 2, wherein said at least one roller is rotatably mounted between two pistons, each said piston being arranged to be moved between an inwardly retracted position in the body and an outwardly deployed condition relative to the body in response to pressurisation of fluid in the body.
 12. An apparatus according to claim 2, wherein said at least one roller is rotatably mounted between two mounting members, each said mounting member being disposed on respective biasing means to enable each said mounting member to move between an inwardly retracted position in the body and an outwardly deployed condition relative to the body.
 13. An apparatus according to claim 12, wherein said biasing means comprises at least one disk spring mounted between the respective mounting member and the body.
 14. An apparatus according to claim 2, further comprising a plurality of rollers disposed at different locations around the body.
 15. An apparatus according to claim 2, wherein the surface engagement means comprises a thread disposed on an outer surface of said at least one roller.
 16. An apparatus according to claim 2, wherein the surface engagement means comprises a plurality of protrusions disposed on an outer surface of said at least one roller.
 17. A drill string comprising a downhole expandable drive reamer apparatus according to claim
 2. 